April 2000 arXiv papers — page 18

M. H. Siegel, S. R. Majewski

We present the first comprehensive catalogue of variable stars in the Leo II dwarf spheroidal galaxy. We have identified 148 RR Lyrae type variables, of which 140 were amenable to derivation of variability parameters with our data. We have also confirmed the existence of four anomalous Cepheids as identified in previous studies. The average period of the RR

Kenji Bekki, Masashi Chiba

Motivated by the recently improved knowledge on the kinematic and chemical properties of the Galactic metal-poor stars, we present the numerical simulation for the formation of the Galactic stellar halo to interpret the observational results. As a model for the Galaxy contraction, we adopt the currently standard theory of galaxy formation based on the hierar

Jochen Weller

In a model recently proposed by Albrecht and Skordis it was suggested that the observed accelerated expansion of the universe could be caused by a scalar field which is trapped in a local minimum of an exponential potential modified by a polynomial prefactor. We show that scalar field cosmologies with this kind of local minimum in the potential are stable an

Michael Melles

In future collider experiments at the TeV scale, large logarithmic corrections originating from massive boson exchange can lead to significant corrections to observable cross sections. Recently double logarithms of the Sudakov-type were resummed for spontaneously broken gauge theories and found to exponentiate. In this paper we use the virtual contributions

I. Brevik, B. Jensen, K. A. Milton

It is shown that recent criticism by C. R. Hagen (hep-th/9902057) questioning the validity of stress tensor treatments of the Casimir energy for space divided into two parts by a spherical boundary is without foundation.

Roman Scoccimarro

The bispectrum is the lowest-order statistic sensitive to the shape of structures generated by gravitational instability and is a potentially powerful probe of galaxy biasing and the Gaussianity of primordial fluctuations. Although the evolution of the bispectrum is well understood theoretically from non-linear perturbation theory and numerical simulations,

Sean M. Carroll

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero) vacuum energy.

Michael D. Gladders, H. K. C. Yee

Numerous methods for finding clusters at moderate to high redshifts have been proposed in recent years, at wavelengths ranging from radio to X-rays. In this paper we describe a new method for detecting clusters in two-band optical/near-IR imaging data. The method relies upon the observation that all rich clusters, at all redshifts observed so far, appear to

Andrea Rocco, Ute Ebert, Wim van Saarloos

We study the propagation of a ``pulled'' front with multiplicative noise that is created by a local perturbation of an unstable state. Unlike a front propagating into a metastable state, where a separation of time scales for sufficiently large $t$ creates a diffusive wandering of the front position about its mean, we predict that for so-called pulled

R. Carretero-González, S. Ørstavik, J. Stark

We describe methods of estimating the entire Lyapunov spectrum of a spatially extended system from multivariate time-series observations. Provided that the coupling in the system is short range, the Jacobian has a banded structure and can be estimated using spatially localised reconstructions in low embedding dimensions. This circumvents the ``curse of dimen

A. Hart, M. Laine, O. Philipsen

We use a perturbatively derived effective field theory and three-dimensional lattice simulations to determine the longest static correlation lengths in the deconfined QCD plasma phase at high temperatures (T\gsim 2 Tc) and finite densities (μ\lsim 4 T). For vanishing chemical potential, we refine a previous determination of the Debye screening length, and de

A. V. Belitsky, D. Müller, L. Niedermeier, A. Schäfer

We calculate spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering at leading twist-two level. The measurement of these asymmetries gives an access to the imaginary and real part of all deeply virtual Compton scattering amplitudes. We note that a consistent description of this process requires taking into account twist-three contributi

Elena Caceres, Rafael Hernandez

We study the quark-antiquark interaction in the large N limit of the superconformal field theory on D-3branes at a Calabi-Yau conical singularity. We compute the Wilson loop in the AdS_5xT^{11} supergravity background for the SU(2N)x SU(2N) theory. We also calculate the Wilson loop for the Higgs phase where the gauge group is broken to SU(N)x SU(N)x SU_D(N).

Jonathan L. Feng, Konstantin T. Matchev, Frank Wilczek

In recent work, it has been argued that multi-TeV masses for scalar superpartners are not unnatural. Indeed, they appear to have significant phenomenological virtues. Here we explore the implications of such `focus point' supersymmetry for the dark matter problem. We find that constraints on relic densities do not place upper bounds on neutralino or scal

Sigbjorn Hervik

In this paper we study a class of inhomogeneous cosmological models which is a modified version of what is usually called the Lemaître-Tolman model. We assume that we have a space with 2-dimensional locally homogeneous spacelike surfaces. In addition we assume they are compact. Classically we investigate both homogeneous and inhomogeneous spacetimes which th

R. Burioni, D. Cassi, I. Meccoli, M. Rasetti

We show that spatial Bose-Einstein condensation of non-interacting bosons occurs in dimension d < 2 over discrete structures with inhomogeneous topology and with no need of external confining potentials. Josephson junction arrays provide a physical realization of this mechanism. The topological origin of the phenomenon may open the way to the engineering of

Takeshi Tanaka, Rashid G. Nazmitdinov, Kazuo Iwasawa

High spin states of ^{32}S$ and ^{56}Ni are investigated by means of the cranking Hartree-Fock method with the Gogny interaction without imposing a restriction on the axial reflection symmetry. It was found that a non-axial octupole deformation of the Y_{31} type becomes important in the yrast states of ^{32}S. A similar effect is predicted for the nucleus ^

Yoram Burak, David Andelman

A model for ionic solutions with an attractive short-range pair interaction between the ions is presented. The short-range interaction is accounted for by adding a quadratic non-local term to the Poisson-Boltzmann free energy. The model is used to study solvent effects in a planar electric double layer. The counter-ion density is found to increase near the c

N. Ishibashi, S. Iso, H. Kawai, Y. Kitazawa

We identify the effective string scale of noncommutative Yang-Mills theory (NCYM) with the noncommutativity scale through its dual supergravity description. We argue that Newton&#39;s force law may be obtained with 4 dimensional NCYM with maximal SUSY. It provides a nonperturbative compactification mechanism of IIB matrix model. We can associate NCYM with th

C. P. Korthals Altes, A. Kovner

We discuss the relation between the deconfining phase transition in gauge theories and the realization of the magnetic Z(N) symmetry. At low temperature the Z(N) symmetry is spontaneously broken while above the phase transition it is restored. This is intimately related to the change of behaviour of the spatial &#39;t Hooft loop discussed in hep-ph/9909516.

N. E. Hussey, S. Nakamae, K. Behnia, H. Takagi

We report here measurements of the in-plane thermal conductivity K(T) of the underdoped cuprate YBa2Cu4O8 (Y124) below 1K. K(T) is shown to follow a simple, phononic T^3 dependence at the lowest temperatures for both current directions, with a negligible linear, quasiparticle contribution. This observation is in marked contrast with behavior reported in opti

M. Cadoni, C. N. Colacino

We study the thermodynamical and geometrical behaviour of the black holes that arise as solutions of the heterotic string action. We discuss the near-horizon scaling behaviour of the solutions that are described by two-dimensional Anti-de Sitter Space AdS(2). We find that finite-energy excitations of AdS(2) are suppressed only for scaling limits characterise

Michael McNeil Forbes, Ariel R. Zhitnitsky

We propose a mechanism to generate large-scale magnetic fields with correlation lengths of 100 kpc. Domain walls with QCD scale internal structure form and coalesce obtaining Hubble scale correlations and align nucleon spins. Due to strong CP violation, nucleons in these walls have anomalous electric and magnetic dipole moments and thus the walls are ferroma

K. Tsushima, A. Sibirtsev, A. W. Thomas

Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were cal

Sven Bergmann, H. V. Klapdor-Kleingrothaus, Heinrich Päs

Mixing between bosons that transform differently under the standard model gauge group, but identically under its unbroken subgroup, can induce interactions that violate the total lepton number. We discuss four-fermion operators that mediate lepton number violating neutrino interactions both in a model-independent framework and within supersymmetry (SUSY) wit

P. Draggiotis, A. van Hameren, R. Kleiss

We present an algorithm to generate any number of random massless momenta in phase space, with a distribution that contains the kinematical pole structure that is typically found in multi-parton QCD-processes. As an application, we calculate the cross-section of some \eplus\eminus \to partons processes, and compare SARGE&#39;s performance with that of the un

F. Guerin

An effective theory for the soft field modes in hot QCD has been obtained recently by integrating out the field modes of momenta of order T and g T. The mean hard particle distribution obeys a transport equation with a collision term. The scale that comes out for the soft field is g^2 T ln 1/g . N-gluon soft amplitudes are shown to be a sum of tree diagrams

Paolo Tombesi, Vittorio Giovannetti, David Vitali

An all-optical feedback scheme in which the output of a cavity mode is used to influence the dynamics of another cavity mode is considered. We show that under ideal conditions, perfect preservation against decoherence of a generic quantum state of the source mode can be achieved.

G. Cassinelli, G. M. D&#39;Ariano, E. De Vito, A. Levrero

The paper is devoted to the mathematical foundation of the quantum tomography using the theory of square-integrable representations of unimodular Lie groups.

Mauro Fortunato, Paolo Tombesi, David Vitali, Jean-Michel Raimond

We review the use of quantum feedback for combatting the decoherence of Schroedinger-cat-like states in electromagnetic cavities, with special emphasys on our recent proposal of an automatic mechanism based on the injection of appropriately prepared ``probe&#39;&#39; and ``feedback&#39;&#39; Rydberg atoms. In the latter scheme, the information transmission f

Silas R. Beane, Paulo F. Bedaque, Martin J. Savage

The renormalization group is used to resum leading logarithmic contributions of the form alpha_s^{n+1} beta_0^n log^n (Delta/mu) to the gap equation appropriate for high density QCD. The scale dependence of the strong coupling constant alpha_s increases the gap by a factor of exp(33/16 (pi^2/4 - 1)) ~ 20 in the small coupling limit.

A. Mariano

A dynamical model based on effective Lagrangians is proposed to describe the bremsstrahlung reaction $ πN \to πN γ$ at low energies. The $Δ(1232)$ degrees of freedom are incorporated in a way consistent with both, electromagnetic gauge invariance and invariance under contact transformations. The model also includes the initial and final state rescattering of

Soojae Im, J. Meng

The nucleon density distributions and the thickness of pure neutron matter in Ca isotopes were systematically studied using the Skyrme-Hartree-Fock model (SHF) from the $β$-stability line to the neutron drip-line. The pure neutron matter, related with the neutron skin or halo, was shown to depend not only on the Fermi levels of the neutrons but also on the o

A. Echeverrí a-Enrí quez, M. C. Muñoz-Lecanda, N. Román-Roy

In the jet bundle description of Field Theories (multisymplectic models, in particular), there are several choices for the multimomentum bundle where the covariant Hamiltonian formalism takes place. As a consequence, several proposals for this formalism can be stated, and, on each one of them, the differentiable structures needed for setting the formalism ar

Michael Hutchings

In two previous papers with Yi-Jen Lee, we defined and computed a notion of Reidemeister torsion for the Morse theory of closed 1-forms on a finite dimensional manifold. The present paper gives an a priori proof that this Morse theory invariant is a topological invariant. It is hoped that this will provide a model for possible generalizations to Floer theory

J. Fuchs, C. Schweigert

Conformal blocks form a system of vector bundles over the moduli space of complex curves with marked points. We discuss various aspects of these bundles. In particular, we present conjectures about the dimensions of sub-bundles. They imply a Verlinde formula for non-simply connected groups like PGL(n,C). We then explain how conformal blocks enter in the cons

Maciej Dunajski, Lionel J. Mason, Paul Tod

It is shown that Einstein-Weyl (EW) equations in 2+1 dimensions contain the dispersionless Kadomtsev-Petviashvili (dKP) equation as a special case: If an EW structure admits a constant weighted vector then it is locally given by $h=d y^2-4d xd t-4ud t^2, ν=-4u_xd t$, where $u=u(x, y, t)$ satisfies the dKP equation $(u_t-uu_x)_x=u_{yy}$. Linearised solutions

Stefan Boller

This paper generalizes the results obtained in an earlier paper (math.OA/0003087) for finite factors to infinite but still semifinite factors. First we give a characterization of cyclic and separating vectors for infinite semifinite factors in terms of operators associated with this vector and being affiliated with the factor. Further we show how this operat

Bernhard Kroetz, Gestur Olafsson

In this paper we prove the product formula for the c-function of non-compactly causal symmetric spaces.

Bernhard Kroetz

In this paper we generalize Harish Chandra&#39;s formula for the formal dimension of a representation of the holomorphic discrete series of a hermitian Lie group $G$ to semisimple symmetric spaces $G/H$.

F. Malikov, V. Schechtman

We reproduce the quantum cohomology of toric varieties (and of some hypersurfaces in projective spaces) as the cohomology of certain vertex algebras with differential. The deformation technique allows us to compute the cohomology of the chiral de Rham complex over the projective space.

A. Alekseev, A. P. Polychronakos, M. Smedbäck

We consider a model of a black hole consisting of a number of elementary components. Examples of such models occur in the Ashtekar&#39;s approach to canonical Quantum Gravity and in M-theory. We show that treating the elementary components as completely distinguishable leads to the area law for the black hole entropy. Contrary to previous results, we show th

V. E. Kuzmichev, V. V. Kuzmichev

In a model of nonlinear system of three scalar fields the problem on dynamics of a massive particle moving in effective potential provided by two relativistic fields is solving. The potentials for these fields are chosen in the form of anti-Higgs and Higgs potentials. It is shown that the effective potential has the shape of two-hump barrier localized in spa

V. E. Kuzmichev, V. V. Kuzmichev

The idea of ``soft&#39;&#39; confinement when the lifetime of hadron with respect to quark-gluon channel of decay is greater or at least of the order of some characteristic time for our Universe is considered. Within the framework of a model of three nonlinearly interacting fields the explicit form of an effective potential is found. It provides the confinem

J. F. Gunion, B. Grzadkowski

We review the possibilities that the Kaluza-Klein excitations of graviton states induce electroweak symmetry breaking and that electroweak symmetry breaking could have a large impact on KK phenomenology.

H. Weigel, L. Gamberg

We outline a consistent regularization procedure to compute hadron structure functions within bosonized chiral quark models. We impose the Pauli--Villars scheme, which reproduces the chiral anomaly, to regularize the bosonized action. We derive the Compton amplitude from this action and utilize the Bjorken limit to extract structure functions that are consis

C. S. Kim, H. Yamamoto

First, we give summary of the present values of CKM matrix elements. Then, we discuss whether CKM matrix is unitary or not, and how we can find out if it is not unitary.

D. Klabucar, K. Kumericki, B. Melic, I. Picek

On top of its valence quarks, the full nucleon ground state may contain appreciable admixture of s-\bar{s} pairs already at small momentum transfers. This paper discusses strangeness in the mean-field type of nucleon models, and exemplifies this by explicit calculations in the MIT bag model enriched by the presence of instantons. We calculate the instanton c

K. Sridhar

In this talk, I first present the motivation for theories wherein extra spacetime dimensions can be compactified to have large magnitudes. In particular, I discuss the Arkani-Hamed, Dimopoulos, Dvali (ADD) scenario. I present the constraints that have been derived on these models from current experiments and the expectations from future colliders. I concentr

K. Enqvist, A. Jokinen, J. McDonald

Coherently oscillating scalar condensates formed along flat directions of the MSSM scalar potential are unstable with respect to spatial perturbations if the potential is flatter than phi^2, resulting in the formation of non-topological solitons such as Q-balls. Using renormalization group we calculate the corrections to the phi^2 potential for a range of fl

S. Bergmann, M. M. Guzzo, P. C. de Holanda, P. I. Krastev

We analyze the current status of the solution to the solar neutrino problem based both on: a) non-standard flavor changing neutrino interactions (FCNI) and b) non-universal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the sun as well as in the earth provide a good fit not only to the total rate measured by all solar

M. Bleicher, M. Belkacem, S. A. Bass, S. Soff

The centrality dependence of the antiproton per participant ratio is studied in Pb(160 AGeV)+Pb reactions. Antiproton production in collisions of heavy nuclei at the CERN/SPS seems considerably enhanced as compared to conventional hadronic physics, given by the antiproton production rates in $pp$ and antiproton annihilation in $\bar{p}p$ reactions. This enha

Bohdan Grzadkowski, John F. Gunion, Jacek Pliszka

We study a possibility of a measurement of muon Yukawa couplings in s-channel Higgs boson production at a muon collider with transversely polarized beams. We investigate sensitivity to the relative size of the CP-odd and CP-even muon Yukawa couplings. Provided the event rate observed justify the operation of the $μ^+μ^-$ Higgs boson factory, we have found th

Y. Kulchitsky

Hadron energy reconstruction for the Atlas barrel prototype combined calorimeter, consisting of the lead-liquid argon electromagnetic part and the iron-scintillator hadronic part, in the framework of the non-parametrical method has been fulfilled. This method uses only the known e/h ratios and the electron calibration constants and does not require the deter

Santiago E. Perez Bergliaffa

Einstein&#39;s equations for a 4+n-dimensional inhomogeneous space-time are presented, and a special family of solutions is exhibited for an arbitrary n. The solutions depend on two arbitrary functions of time. The time development of a particular member of this family is studied. This solution exhibits a singularity at t=0 and dynamical compactification of

Nathalie Deruelle, Tomas Dolezel

We first illustrate on a simple example how, in existing brane cosmological models, the connection of a &#39;bulk&#39; region to its mirror image creates matter on the &#39;brane&#39;. Next, we present a cosmological model with no $Z_2$ symmetry which is a spherical symmetric &#39;shell&#39; separating two metrically different 5-dimensional anti-de Sitter re

Alan Barnes

In a recent paper Carot et al. considered carefully the definition of cylindrical symmetry as a specialisation of the case of axial symmetry. One of their propositions states that if there is a second Killing vector, which together with the one generating the axial symmetry, forms the basis of a two-dimensional Lie algebra, then the two Killing vectors must

Marc Mars

We obtain a geometrical condition on vacuum, stationary, asymptotically flat spacetimes which is necessary and sufficient for the spacetime to be locally isometric to Kerr. Namely, we prove a theorem stating that an asymptotically flat, stationary, vacuum spacetime such that the so-called Killing form is an eigenvector of the self-dual Weyl tensor must be lo

Giampiero Esposito

When quantum fields are studied on manifolds with boundary, the corresponding one-loop quantum theory for bosonic gauge fields with linear covariant gauges needs the assignment of suitable boundary conditions for elliptic differential operators of Laplace type. There are however deep reasons to modify such a scheme and allow for pseudo-differential boundary-

H. Won, K. Maki

Quasiparticle spectrum associated with the nodal structure in d-wave superconductors is of great interest. We study theoretically the quasi-particle spectrum in a planar magnetic field, where the effect of the magnetic field is treated in terms of the Doppler shift. We obtain the angular dependent specific heat in the presence of a planar magnetic field and

Karl Haller, Tom Kennedy

We consider the Falicov-Kimball model in two dimensions in the neutral case, i.e, the number of mobile electrons is equal to the number of ions. For rational densities between 1/3 and 2/5 we prove that the ground state is periodic if the strength of the attraction between the ions and electrons is large enough. The periodic ground state is given by taking th

Alex J. Levine, T. C. Lubensky

We study the dynamics of rigid spheres embedded in viscoelastic media and address two questions of importance to microrheology. First we calculate the complete response to an external force of a single bead in a homogeneous elastic network viscously coupled to an incompressible fluid. From this response function we find the frequency range where the standard

D. Lacoste, F. Donatini, S. Neveu, J. A. Serughetti

An experimental and theoretical study on the Photonic Hall Effect (PHE) in liquid and gelled samples of ferrofluids is presented. The ferrofluids are aqueous colloidal suspensions of Fe(_{2})CoO(_{4}) particles, which can be considered as anisotropic and absorbing Rayleigh scatterers. The PHE is found to be produced by the orientation of the magnetic moments

D. Lacoste

This article presents a derivation of the transport mean free path for magneto-transverse light diffusion, $\ell^*_\perp$, in an arbitrary random mixture of Faraday-active and non-Faraday active Mie scatterers. This derivation is based on the standard radiative transfer equation. The expression of the transport mean free path obtained previously from the Bet

V. M. Avdjukhina, A. A. Katsnelson, G. P. Revkevich, E. A. Goron

It has been discovered that kinetics of structural changes in Pd and Pd-alloys under the influence of dissolved hydrogen seems to be non-trivial. As a rule, structural changes in these systems include correlation changes of co-existing phases concentration and the defect structure character. These changes have the stage character. Basic stages are: incubatio

M. Koskinen, M. Manninen, B. Mottelson, S. M. Reimann

One can confine the two-dimensional electron gas in semiconductor heterostructures electrostatically or by etching techniques such that a small electron island is formed. These man-made ``artificial atoms&#39;&#39; provide the experimental realization of a text-book example of many-particle physics: a finite number of quantum particles in a trap. Much effort

S. M. Reimann, M. Koskinen, M. Manninen

It was recently argued that in small quantum dots the electrons could crystallize at much higher densities than in the infinite two-dimensional electron gas. We compare predictions that the onset of spin polarization and the formation of Wigner molecules occurs at a density parameter $r_s\approx 4 a_B^*$ to the results of a straight-forward diagonalization o

Gaetan Caldara, Bhargavi Srinivasan, Dima Shepelyansky

We study the ground state of the two-dimensional (2D) disordered Hubbard model by means of the projector quantum Monte Carlo (PQMC) method. This approach allows us to investigate the ground state properties of this model for lattice sizes up to $10 \times 10$, at quarter filling, for a broad range of interaction and disorder strengths. Our results show that

Yong Kong

In order to investigate the phase stability of equiatomic FeN compounds and the structure-dependent magnetic properties, the electronic structure and total energy of FeN with NaCl, ZnS and CsCl structures and various magnetic configurations are calculated using the first-principles TB-LMTO-ASA method. Among all the FeN phases considered, the antiferromagneti

J. P. Boucher, M. Takigawa

A model of mobile-bond defects is tentatively proposed to analyze the &#34;anomalies&#34; observed on the NMR spectrum of the quantum Heisenberg chains of Sr2CuO3. A bond-defect is a local change in the exchange coupling. It results in a local alternating magnetization (LAM), which when the defect moves, creates a flipping process of the local field seen by

S. Potting, O. Zobay, P. Meystre, E. M. Wright

In previous work we showed that bright atomic solitons can arise in spinor Bose-Einstein condensates in the form of gap solitons even for repulsive many-body interactions. Here we further explore the properties of atomic gap solitons and show that their internal structure can be used to both excite them and control their center-of-mass motion using applied l

Guang-Ming Zhang, Qiang Gu, Lu Yu

A simplified version of the symmetric Kondo lattice model, the Kondo necklace model, is studied by using a representation of impurity and conduction electron spins in terms of local Kondo singlet and triplet operators. Within a mean field theory, a spin gap always appears in the spin triplet excitation spectrum in 1D, leading to a Kondo spin liquid state for

C. K. Law, C. M. Chan, P. T. Leung, M. -C. Chu

We present an exact analytic solution of a nonlinear Schrödinger field interacting with a moving potential (obstacle) at supersonic speed. We show that the field forms a stable shape-invariant structure localized around the obstacle --- a dressing effect that protects the field against excitations by the obstacle.

E. Ardonne, P. Bouwknegt, K. Schoutens

We study excitations in edge theories for non-abelian quantum Hall states, focussing on the spin polarized states proposed by Read and Rezayi and on the spin singlet states proposed by two of the authors. By studying the exclusion statistics properties of edge-electrons and edge-quasiholes, we arrive at a novel K-matrix structure. Interestingly, the duality

S. C. Trager, S. M. Faber, G. Worthey, J. J. Gonzalez

We analyze single-stellar-population (SSP) equivalent parameters for 50 local elliptical galaxies as a function of their structural parameters. These galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H], log t, log $σ$, and [E/Fe]. SSP age and velocity dispersion can be taken as the two independent parameters that specify a galaxy&#39

Woong-Tae Kim, Eve C. Ostriker

We investigate shear and buoyancy instabilities in radially stratified, magnetized, cylindrical flows, for application to magnetocentrifugally driven winds and to magnetized accretion disks. We identify and study nine principal types of instabilities/overstabilities. When magnetic fields are predominantly toroidal, as in protostellar winds, the system exhibi

Markus J. Aschwanden, Nariaki Nitta

We investigate the effect of hydrostatic scale heights $λ(T)$ in coronal loops on the determination of the vertical temperature structure $T(h)$ of the solar corona. Every method that determines an average temperature at a particular line-of-sight from optically thin emission (e.g. in EUV or soft X-ray wavelengths) of a mutli-temperature plasma, is subject t

B. P. Holden, C. Adami, R. C. Nichol, F. J. Castander

We present the first dynamical study of the optically selected Palomar Distant Cluster Survey (PDCS). We show that eleven out of twelve PDCS clusters we observed are real over-densities of galaxies. Most clusters have velocity dispersions appropriate for clusters of galaxies. However, we find a fraction (1/3) of objects in the PDCS which have velocity disper

Charles C. Dyer, Chris Oliwa

Contrary to a claim, the Schwarzschild solution insertion in an expanding universe model, the so called &#34;Swiss cheese&#34; model, does not possess an extrinsic curvature discontinuity. We show that both the intrinsic metric and the extrinsic curvature are continuous, and point out the error that led to the claim.

David S. Graff, B. Scott Gaudi

We propose a direct method to detect close-in giant planets orbiting stars in the Galactic bulge. This method uses caustic-crossing binary microlensing events discovered by survey teams monitoring the bulge to measure light from a planet orbiting the source star. When the planet crosses the caustic, it is more magnified than the source star; its light is mag

Kerstin Weis

WRA 751 is an evolved massive star in our Galaxy closely resembling Luminous Blue Variable stars (LBVs). It is surrounded by a nitrogen enriched nebula of ab out 23&#34; diameter. A comparative study of the nebula&#39;s morphology and kinematics is presented, it supports - together with spectroscopical evidence - the classification of WRA 751 as a LBV. Image

R. Scoccimarro, H. A. Feldman, J. N. Fry, J. Frieman

We compute the bispectrum for the galaxy distribution in the IRAS QDOT, 2Jy, and 1.2Jy redshift catalogs for wavenumbers 0.05<k<0.2 h/Mpc and compare the results with predictions from gravitational instability in perturbation theory. Taking into account redshift space distortions, nonlinear evolution, the survey selection function, and discreteness and finit

Claudio Pernechele, Favio Bortoletto, Paolo Conconi, Daniele Gardiol

In this paper a preliminary design for a prime focus corrector to be mounted at the Telescopio Nazionale Galileo (TNG) is presented. The telescope is located on La Palma (Canary Islands) and has a primary mirror of 3.5 m with a hyperbolic sag. Two optical designs have been considered in order to exploit detectors with 1k x 1k and 2k x 2k pixels. Each design

R. R. Rafikov, R. M. Kulsrud

The possibility of the magnetic flux expulsion from the Galaxy in the superbubble (SB) explosions, important for the Alpha-Omega dynamo, is considered. Special emphasis is put on the investigation of the downsliding of the matter from the top of the shell formed by the SB explosion which is able to influence the kinematics of the shell. It is shown that eith

A. Tarchi, N. Neininger, A. Greve, U. Klein

We present a high-resolution 5-GHz radio continuum map of the starburst galaxy NGC 2146 made with MERLIN and the VLA, in a search of radio supernovae and supernova remnants expected to be already produced by the most massive stars in the starburst. At 5 GHz, about 20 point sources were detected earlier by Glendenning & Kronberg (1986) in the central 800 pc o

G. Cauzzi, A. Falchi, R. Falciani

We analyze the temporal behavior of Network Bright Points (NBPs), present in the solar atmosphere, using a set of data acquired during coordinated observations between ground-based observatories (mainly at the NSO/Sacramento Peak) and the Michelson Doppler Interferometer onboard SOHO. We find that, at any time during the observational sequence, all the NBPs

Orsola De Marco, W. Schmutz, P. A. Crowther, D. J. Hillier

In this paper we derive stellar parameters for the Wolf-Rayet star in the gamma Velorum binary system (WR11), from a detailed non-LTE model of its optical and infrared spectra. Compared to the study of Schaerer et al., the parameters of the WC8 star are revised to a hotter effective temperature (Teff~57kK),a higher luminosity (log(L/Lsun = 5.00), and a lower

M. Axenides, E. G. Floratos, L. Perivolaropoulos

Newton&#39;s law gets modified in the presence of a cosmological constant by a small repulsive term (antigarvity) that is proportional to the distance. Assuming a value of the cosmological constant consistent with the recent SnIa data ($Λ\simeq 10^{-52} m^{-2}$) we investigate the significance of this term on various astrophysical scales. We find that on gal

J. U. Fynbo, I. Burud, P. Moller

We present deep imaging in the U, B and I bands obtained under excellent seeing conditions of the double quasar Q0151+048A,B and of the Damped Ly-alpha (DLA) absorbing galaxy at z(abs) = 1.9342 named S4. We analyse the data employing two separate and independent methods. First we deconvolve the images using the MCS algorithm, secondly we decompose the images

Michael L. Balogh, Julio F. Navarro, Simon L. Morris

We examine the origin of clustercentric gradients in the star formation rates and colors of rich cluster galaxies within the context of a simple model where clusters are built through the ongoing accretion of field galaxies. The model assumes that after galaxies enter the cluster their star formation rates decline on a timescale of a few Gyrs, the typical ga

F. Zagury

The spectrum of five stars is analysed and explained by the superimposition of two components. One is the extinction of the direct starlight, with an extinction coefficient A which varies as the inverse of the wavelength across all the UV. This linear dependence of extinction upon the inverse of wavelength prolongs to the UV the well known relation which exi

Wolfgang J. Duschl, Peter A. Strittmatter, Peter L. Biermann

We propose a generalized accretion disk viscosity prescription based on hydrodynamically driven turbulence at the critical effective Reynolds number. This approach is consistent with recent re-analysis by Richard & Zahn (1999) of experimental results on turbulent Couette-Taylor flows. This new $β$-viscosity formulation is applied to both selfgravitating and

Mikhail S. Plyushchay

The topological nature of Chern-Simons term describing the interaction of a charge with magnetic monopole is manifested in two ways: it changes the plane dynamical geometry of a free particle for the cone dynamical geometry without distorting the free (geodesic) character of the motion, and in the limit of zero charge&#39;s mass it describes a spin system. T

Heribert Weigert

This paper presents a solution to the nonlinear small x ``projectile side&#39;&#39; evolution equations as derived by Balitskii in 1996. The solution is based on functional Fokker-Planck methods. The fixed point at small x is explicitly calculated and all correlation functions in this limit are determined. They show clear saturation and unitarization propert

J. J. Salzer, C. Gronwall, V. A. Lipovetsky, A. Kniazev

The KPNO International Spectroscopic Survey (KISS) is a new objective-prism survey for extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys that were carried out with Schmidt telescopes using photographic plates with the advantages of modern CCD detectors. It is the first purely digital objective-pr

Peter Gorham, David Saltzberg, Paul Schoessow, Wei Gai

We report on measurements of 11-18 cm wavelength radio emission from interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield Accelerator. The electrons were observed both in a configuration where they produced primarily transition radiation from an aluminum foil, and in a configuration designed for the electrons to produce Cherenkov radiati

F. Zagury

This paper presents an analysis of the UV spectrum of some nebulae with clearly identified illuminating stars, all observed by the IUE satellite. The data show remarkable properties of the UV spectrum of the nebulae. Each spectrum is the product of the star spectrum and a linear function of 1/lambda. There is no peculiar behaviour in the spectrums at 2200A:

Arne Brataas, X. H. Wang

The current through ferromagnetic single-electron transistors (SET&#39;s) is considered. Using path integrals the linear response conductance is formulated as a function of the tunnel conductance vs. quantum conductance and the temperature vs. Coulomb charging energy. The magneto-resistance of ferromagnet-normal metal-ferromagnet (F-N-F) SET&#39;s is almost

L. Pilo, R. Rattazzi, A. Zaffaroni

We clarify some general issues in models where gravity is localized at intermediate distances. We introduce the radion mode, which is usually neglected, and we point out that its role in the model is crucial. We show that the brane bending effects discussed in the literature can be obtained in a formalism where the physical origin is manifest. The model viol

A. Cruz, J. Pech, A. Tarancon, P. Tellez

The use of last generation Programmable Electronic Components makes possible the construction of very powerful and competitive special purpose computers. We have designed, constructed and tested a three-dimensional Spin Glass model dedicated machine, which consists of 12 identical boards. Each single board can simulate 8 different systems, updating all the s